Implemented the Word64Popcnt TurboFan operator for x64.

src/compiler/instruction-selector.cc

Index: src/compiler/instruction-selector.cc
diff --git a/src/compiler/instruction-selector.cc b/src/compiler/instruction-selector.cc
index 5a6088a193c8a169374f3a2974926435b9af26ec..067f886242f2ee6de45a644ad3e9e910232569ca 100644
--- a/src/compiler/instruction-selector.cc
+++ b/src/compiler/instruction-selector.cc
@@ -722,6 +722,8 @@ void InstructionSelector::VisitNode(Node* node) {
       return MarkAsWord32(node), VisitWord32Ctz(node);
     case IrOpcode::kWord32Popcnt:
       return MarkAsWord32(node), VisitWord32Popcnt(node);
+    case IrOpcode::kWord64Popcnt:
+      return MarkAsWord32(node), VisitWord64Popcnt(node);
     case IrOpcode::kWord64And:
       return MarkAsWord64(node), VisitWord64And(node);
     case IrOpcode::kWord64Or:
@@ -981,6 +983,9 @@ void InstructionSelector::VisitWord64Clz(Node* node) { UNIMPLEMENTED(); }
 void InstructionSelector::VisitWord64Ctz(Node* node) { UNIMPLEMENTED(); }
 
 
+void InstructionSelector::VisitWord64Popcnt(Node* node) { UNIMPLEMENTED(); }
+
+
 void InstructionSelector::VisitWord64Equal(Node* node) { UNIMPLEMENTED(); }